When conducting a chemotaxis assay to test if the experimental RNAi treatment affected C. elegans, what is the purpose of using sodium azide on the chemotaxis assay plates

It is a metabolic inhibitors.

Explanation:

The purpose of using sodium azide on the chemotaxis assay plates causes stress protein expression and creates the ability to tolerate high temperature. Sodium azide inhibits oxidative phosphorylation through inhibition of cytochrome oxidase that result in a rapid depletion of ATP. Exposure to the metabolic inhibitor i.e. sodium azide causes stress protein expression and tolerance to high temperatures in the nematode Caenorhabditis elegans.